Diels-Alder cycloaddition
specified-next: not executable as a chemically faithful v2 rule yet because geometry/stereochemistry guards are missing.
Interactive Route Player
Use next/prev to step through the route: first the current state is shown without highlight, then the next ownership move is previewed, then the move is executed. If a route snapshot changes several ownership records, the player unfolds them one at a time. Drag a node to fix it; double-click a fixed node to release it.
HEG v2 State Sketches
These panels are rendered from ownership-structured HEG v2 objects. For specified-next examples they are state sketches, not yet products of executable v2 rules.
Diels-Alder substrate HEG sketch
Butadiene plus ethene with explicit pi-pair resources.
Diels-Alder composite snapshot 1
Composite-rule snapshot: first terminal sigma pair is present. This is not meant as an isolated chemical intermediate.
Diels-Alder composite snapshot 2
Composite-rule snapshot: both terminal sigma pairs are present before the final pi-shift snapshot.
Diels-Alder route product
Cyclohexene skeleton: two new sigma pairs and one retained pi pair.
DPO-like Step Panels
Each primitive snapshot is shown as L/K/R. Red marks the ownership edge removed from L, orange marks the halfedge whose owner changes, and green marks the ownership edge created in R. K keeps the common atoms, halfedges, pair objects, and unchanged ownership records. For specified-next examples this is an explanatory span derived from route snapshots, not yet a checked executable rule application.
Diels-Alder composite route step 1
Diels-Alder substrate HEG sketch -> Diels-Alder composite snapshot 1
h11: a5 -> a6; h12: a6 -> a1
L
K
R
Diels-Alder composite route step 2
Diels-Alder composite snapshot 1 -> Diels-Alder composite snapshot 2
h7: a3 -> a4; h8: a4 -> a5
L
K
R
Diels-Alder composite route step 3
Diels-Alder composite snapshot 2 -> Diels-Alder route product
h3: a1 -> a2; h4: a2 -> a3; h7: a4 -> a3; h8: a5 -> a4; h9: a3 -> a4; h10: a4 -> a5; h11: a6 -> a5; h12: a1 -> a6; h13: a5 -> a6; h14: a6 -> a1
L
K
R
Reaction Sketch
Specified as a concerted guarded composite of primitive endpoint moves. Current HEG v2 lacks stereochemical/geometric guards, so this is a mechanism-design target.
Mechanism Flow
Primitive Steps
first terminal diene-dienophile sigma bond forms
concerted pair cycle: pi(diene terminus) + pi(dienophile) -> sigma(C1,C6)
requires s-cis diene and dienophile pi resource
second terminal diene-dienophile sigma bond forms
concerted pair cycle: pi(diene terminus) + pi(dienophile) -> sigma(C4,C5)
requires no pre-existing terminal-dienophile bonds
internal diene pi bond shifts to cyclohexene pi bond
concerted pair cycle: pi(C2,C3) -> pi(cyclohexene)
requires cyclic ordering and admissible valence after composite
Guards and Alternatives
Guards
- diene must be in s-cis topology.
- dienophile must provide pi resource.
- new sigma bonds must be absent before application.
- regio- and stereochemical constraints are not yet represented by current labels.
Route probes
- endo/exo and regioisomeric paths are genuine alternatives, but need geometry/stereochemistry metadata.
- Without those guards a graph-only expansion would overgenerate.